POLYMERASE CHAIN REACTION-BASED APPROACHES FOR DETECTION OF ALLELIC LOSS IN THE P53 TUMOR-SUPPRESSOR GENE IN COLON NEOPLASMS

Objectives: Inactivation of the p53 tumor suppressor gene is considere d to be a late event involved in the malignant transformation of color ectal adenoma to cancer. Thus, its detection is thought to provide use ful information for the clinical management of colorectal neoplasms. W e devised a rapid screening test for allelic loss of the p53 gene by n on-radioisotopic single-strand conformation polymorphism analysis. Met hods: Biopsy materials from 119 colorectal tumors obtained at endoscop y were examined. Three intragenic polymorphic sites were amplified by polymerase chain reaction using DNA extracted from these materials, an d amplified DNA fragments were subjected to non-radioisotopic single-s trand conformation polymorphism. Results: This method can detect a los s of heterozygosity (LOH) of the p53 locus from samples containing ove r 40% tumor derived DNA, and the combination of the three polymorphic markers encompassed 62.4% of Japanese patients as informative. In aden ocarcinoma, an LOH was detected in 51.5% (17 of 33) of the samples and in 12.2% (4 of 33) of tubular and/or tubulovillous adenomas. The p53 gene was mutated only in samples carrying an LOH, that is 64.7% (11 of 17) of carcinomas and 25.0% (1 of 4) of adenomas, but there were no m utation in samples retaining both alleles. The presence of an LOH was statistically correlated both with p53 mutation and malignant histolog y (chi(2) test, p < 0.05). Conclusions: This method can detect LOH fro m biopsy material obtained at endoscopy. LOH in the p53 locus precedes mutation of the p53 gene, and its detection provides useful informati on of malignancy in colorectal tumors.